Two-way facsimile communication system



Aug. 12, 1952 G. H. RIDINGS ETAL TWO-WAY FACSIMILE COMMUNICATION SYSTEM 7 SheetsSheet 1 Filed March 3, 1950 WmwOmOUwm .rZMEEDGU UUELO EKHZMU INVENTORS G. H. RIDINGS EULLLEWZdJI.

GNQKOUwE F. s. HALLDEN F. L. CURRIE ATTORNEY '7 Sheets-Sheet 2 G. H. RIDINGS ET AL TWO-WAY FACSIMILE COMMUNICATION SYSTEM Aug. 12, 1952 Filed March 3, 1950 N QE Aug. 12, 1952 e. H. RIDINGS ET AL 2,606,963

TWO-WAY FACSIMTLE COMMUNICATION SYSTEM Filed March 3, 1950 7 Sheets-Sheet s TO FIG. 2

INVENTORS c. H. RIDINGS y F. c. HALLDEN F. L. CURRIE ATTORNEY FIG.3

Aug. 12, 1952 G. H. RIDINGS ETAL TWO-WAY FACSIMILE COMMUNICATION SYSTEM 7' Sheets-Sheet 4 Filed March 5, 1950 Wm: N2 00- INVENTORS G H RIDINGS F. G. HALLDEN F. L. CURRIE ATTORNEY Aug. 12, 1952 G. H. RIDINGS ETAL TWO-WAY FACSIMILE COMMUNICATION SYSTEM 7 Sheets-Sheet 5 Filed March 3, 1950 7 Sheets-Sheet 6 III h 0; O.

G. H. RIDINGS ETAL TWO-WAY FACSIMILE' COMMUNICATION SYSTEM Aug. 12, 1952 Filed March :5, 1950 ATTORNEY Patented Aug. 12, 1952 UNlTED STATES rent orrics TWO-WAY FAcsIMiLE COMMUNICATION I SYSTEM 7 Application March 3, 1950, Serial No. 147,372

(Cl. i78 -6.6)

26 Claims. 1

This invention relates to the art of facsimile telegraphic communication,-and its general object is to provide a novel system for the speedy two-way transmission of messages between a central telegraph oiiice and the business places of patrons who have subscribed to this service, which eliminates the time formerly required for messenger pick-up and delivery.

The basis of our facsimile telegraph system between patron and main ofiice comprises a transmitter-recorder (usually called a transceiver) in each patrons office adapted to be operatively connected with a concentrator unit in the main office for sending as well as receiving messages. This concentrator unit consists of the required number of transmitters and recorders, at least one of which is usually free to be instantly connected to the patrons machine either to facsimile a telegram to his ofiice or to record a message coming from his machine;

In the present setup of our system the patrons transceiver is a small desk machine which even an unskilled office worker can operate and which, once started, is wholly automatic in its two-way operation for transmitting and receiving messages. This machine is connected with a central telegraph ofiice througha novel control system by which an'operator can instantly plug in a recording machine to receive a patrons message or plug in a transmitter to call the machine of the patron for whom an incoming message is intended. a

The patrons machine is such that when called by the main ofice it automatically sets itself up as a receiver, and when calling the main oilice it automatically becomes a transmitter. This does away with the manually set send-receive switch required in prior facsimile transceivers and simplifies the use of the machine to such an extent that anyone can work it.

When a patron wants to send a telegram to the main ofiice, he simply places the prepared sheet on the scanning drum of his machine and closes the start switch. At the main office the operator gets a signal from the calling machine, whereupon she plugs in one of the recorders and presses a start button. These are the only manual operations required at the two ends of the system for the automatic transmission and recording of a patrons message. When the scanning of this message is completed, both machines are automatically shut down and the operator at the main oilice gets a signal to disconnect the recorder from the line.

When a message for a patron comes in at the main office, the operator loads it on a transmitter, plugs the machine intothe patrons line jack, and presses a call button. This signals the patrons ofiice that the central operator wishes to transmit a message. After placing a recording blank on his drum, the patron merely closes the start switch, whereupon the message starts coming in. After the complete message has been transmittedthe patron gets a signal to advise him of that fact and he acknowledges receipt of the message by pressing a button. At the main ofiice the transmitter is automatically shut down after sending the signatureon the message, and the operator upon receiving the patrons acknowledgment of the message unplugs the transmitter.

The specific features of novelty that characterize our invention will be set forth in the detailed description of the accompanying drawings, which show diagrammatically a practical embodiment of our automatic two-way facsimile system. In these drawings:

Fig.1 is a schematic rep-resentation of our ystem;

Fig. 1A is a section on line lala of Fig. 1 to show the arrangement of certain push buttons and signal lights;

Figs. 2 and 3 together show the transmitter circuits at the main office;

Figs. 4 and 5 together illustrate. the transmitter-receiver circuits of the patrons machine; and

Figs. 6 and 7 together show the recorder circuits at the main office.

The schematic illustration in Fig. 1 gives a general idea of the central office equipment in our system. Eachconcentrator unit of this equipment comprises a group of transmitters and a group of'recorders arranged on either side of a panel I: which carries a series of line jacks I 3 and signal lights M for the patrons machines. This compact arrangement enables a single op erator'to take care of a concentrator unit.

For the purposes of this description we have shown in Fig. 1 a group of four transmitters, four recorders and four patrons machines. Obviously the number .of machines needed at a main oflicewill depend upon the number of patrons it has to serve. For example, in one installation of our system each concentrator is equipped to serve fifty patrons and in thatcase the panel E? has fifty line jacks l3 and as many signal lights I l arranged directly over the jacks.

Every jack and light pair l3-Hl is numbered to identify a particular patron. Thus, jack No. 1

3 connects with the machine of patron No. 1, jack No. 2 is for the machine of patron No. 2, and so forth. In other words, the transmission line of each patron's machine terminates in his particular jack l3 on the concentrator panel l2.

In front of panel 12 is a small table or shelf (Fig. 1A) on which are mounted two sets of push buttons with signal lights, the set on the right being for the transmitters and the left one for the recorders. The transmitter set comprises a front row of call buttons 16, one for each transmitter, a row of white lights ll (called acknowledge lamps), and a row of red busy" lights l8. Similarly, in the recorder set there is a row of start buttons l9, one for each recorder, a row of white lights 20, called end-of-message lamps, and a row of red busy lights 2!. Behind the two rows of red lights is a row of holes 22 for the flexible connecting cables 24 .of the transmitters and a row of holes 23 for the cables 25 of the recorders. Each transmitter cable 24 terminates in.a plug 26'and the recorder cables have each a plug 21.

To promote clearness in Fig. 'l we haveshown the cable and plug of each machine in a schematic way beside it, but actually the transmitter plugs 26 rest on table over the .cable holes 22 and the recorder plugs rest "over the holes 23. Each plug is in a numbered position corresponding to the number of its machine. plug for transmitter No. 1 is in No. 1 position in the row of holes 22, and so on for the other transmitters. The same is true for the position of the recorder plugs 2! over the cable holes 23. In other words, the connection plug of each machine appears on table IS in line with the push button 16 or I.9.of that machine.

General op ration Let us suppose that patron No. 1 wishes to transmit a message to the main oflice. He places the prepared copy around the scanning drum of his machine and closes the start switch. The drum will start to rotate and at the main office the patrons lamp |4No. l is automatically lighted to inform the operator that patron No. 1 has prepared to send a message. The operator inserts the plug 21 of any available recorder (say No. 3) into jack l3No. l, which is directly below the lighted calling lamp. Then she presses the start button l9-No. 3, thereby connecting the transmission circuit of the calling machine with recorder No. 3. The patrons message is now being facsimiled to the main oflice, from where it will be forwarded to its destination. It takes only twominutes or less to dispatch a telegram in this way from a patrons place of business to the main telegraph ofiice.

During the recording of the patrons message the red lamp 2 l--No. 3 (associated with recorder No. 3) remains lighted as an indication to the operator that the patrons message is coming over and is being recorded. When the entire message has been transmitted from the patrons omce, white lamp 28-No. 3 on panel [2 automatically lights to let the operator know that the complete message has been recorded. She thereupon unplugs the recorder and removes from it the recorded facsimile of the transmitted message.

Now let us assume that a message has arrived at the main ofiice for patron No. 4. The operator places this message on the scanning drum 29 of any transmitter that happens to be free, say transmitter No. 1. She first inserts the plug 26 Thus, the i of this transmitter into line Jack I3-i lo. 4 and then she presses the button |6-No. l. The effect of this operation is to sound a buzzer in the patrons machine as a signal that the central ofiice has a message for him. Accordingly, the patron will place a sheet of recording paper on his drum and close the start switch, whereby the machine is automatically set up as a recorder. The closing of the patrons start switch automatically starts the main oiiice transmitter No. l to scan the message on drum 29, while at the saime time the red lamp l 8:No. 1 lights up to indicate that the patron's machine is recording.

When the entire message on drum 29 has been scanned, the patron is automatically advised of that fact by the sounding of his buzzer and the lighting of a lamp. In response to this signal the patron will remove the received telegram from his drum (which has stopped rotating) and operate an acknowledge button. This extinguishes the red busy lamp l8-No. l on the concentrator panel and lights the acknowledge lamp I'I-No. l to indicate to the operator that the patron has received the telegram. The operator now unplugs the transmitter and removes the drum which stopped rotating when the patron operated his acknowledge button. Removal of the drum puts out the acknowledge lamp and shuts off the power from the transmitter, which is now in normal condition ready for the next operation. A supply of transmitter drums 29 may be kept in a chamber 30 below the panel 12.

The transmitter circuits at the main ofiice The foregoing outline of the general operation of our two-way facsimile system will now be followed by a detailed consideration of the novel circuits which make such operation possible, and we shall first take up the transmitter circuits at the main ofiice. In describing these circuits we shall assume that Fig. 3 is placed below Fig. 2 as a continuation thereof.

In Fig. 3 the dotted rectangle TR. represents an optical transmitter like that which forms the subject matter of the copending application of John H. Hackenberg, Serial No. 122,326, filed October 19, 1949. For the purpose of the present specification we have indicated by schematic symbols only such parts of that machine as are necessary to describe the transmitting circuits of our system. Accordingly we need only mention briefly that the transmitter TR has a removable drum 29 which carries the message sheet to be scanned by optical mechanism mounted on a vertically slidable carriage SK. The optical scanning mechanism is represented by an exciter lamp 3! and a photocell 32, the operation of which in facsimile work is well understood.

The carriage SK carries a half-nut 33 mounted on a spring arm 35. which normally holds the half -nut in engagement with a rotary feed screw 35. A synchronous motor 36 drives both the drum 29 and the feed screw 35 at their respective speeds, and a second motor 31 mounted on carriage SK operates a chopper disk (not shown) to interrupt the light beam before it strikes the photocell 32. A solenoid or magnet 38 is adapted when energized to hold the half-nut away from the feed screw 35, and a phase magnet 39 releases when energized a clutch 48 to connect the drum driving shaft 4| with the motor 36. It will therefore be clear that when the magnet 38 is unenergized and the magnet '39 is energized, the motor 36 will rapidly rotate the scanning drum 29 and simultaneously slide the carriage downward to move the optical scanning spot d2 slowly along the message sheet as on the drum.

When the scanning carriage SK has moved through its entire path of travel for long messages, it closes a normally open switch M, which we call the end-of-message switch. The carriage SK may also have mounted thereon a contactor id arranged to engage the metal drum 29 through a hole 43 punched in the message sheet 83 after the signature on a short message. When the contactor 46 touches the grounded drum, the effect is the same as if the switch 3 i were closed by the carriage at the end of its travel. The function performed by switch 44 or the contactor dd when connected to ground will presently be explained. v

In the present instance the carriage SK also controls a switch 35 which is normally open and is held closed by a cam piece on the carriage until the latter has moved down a certain distance from start position. The purpose of holding the switch closed during this interval at the beginning of a scanning cycle will be explained when we describe the circuits of the patrons transceiver in Figs. 4 and 5. A third switch 47 in transmitter TR is normally open and is closed only when a drum 29 is in operative position in the machine. moved, the switch 47 automatically opens for a purpose to be explained later.

The electric power required for the transmitter is indicated by a pair of bus bars A and B, which represent a commercial source of local alternating current power, say of 120 volts and so cycles. The bus bar B may be grounded. A second source of power for certain relay circuits is a positive battery potential and a nega tive battery potential, usually about 120 volts.

To simplify the circuit connections in Figsrz and 3 with the A.-C. and D.-C. power supply, we have used the reference letters A and B at those terminal points that are connected to the bus bars. Likwise, terminals marked with a' plus sign go to positive battery and those marked with a minus sign connect to negative battery.

closed contact 5! of a relay 52 (not energized),

wire 53, through the winding of magnet 38, and by wire 54 to bus bar B. The only other device energized upon insertion of the power plug is a step-down transformer 55 (Fig. 2) which furnishes the filament current for the vacuum tubes of a preamplifier PF. As amplifiers of this type are wellknown both in structure and function, it is sufficient to indicate this apparatus in block form. The heating of the tube filaments in amplifier PF normally keeps this device in standby condition.

The photocell 32 of the optical scanning mech' anism is connected by a wire 56 to the signal input terminal 51 of amplifier PF, and the am plified signal output goes by wires 58 and 59 to n the input terminals of a regulator-inverter RV. We have indicated this apparatus in block diagram only, because any practical construction of regulator-inverter may be used to invertthe scanning signals and regulate the white signal When the drum is re--' 6 or background voltage to such a level that the recording will not show background. This double function of the regulator-inverter in facsimile systems is'well known. and requires no further explanation. The A.-C. power input supplied by conductors 5i and 60 operates a rectifier iii in the apparatus RV to provide plate bat tery for its own tubes and also through wire 62 for the tubes of the amplifier PF. Let-it be noted that the device RV is not energized from the .bus

ductor 60. a

The plug-in cable 24 of each transmitter consists of three conductors 64, 65 and N, which are connected respectively to the tip 61, ring Eli and sleeve 69 of plug 26. The tip and sleeve wires 84 and 66 are connected to the output terminals $3 and 69 of the regulator-inverter RV. The sleeve wire 65 goes to one side of a relay ill. Each of the jacks l3 consists of a tip spring 6?. a ring spring 68', which is normally closed against its fixed contact H, and a sleeve 69. It will be understoodv that when a plug 25 is inserted into any jack is the plug. contacts 6l-63E8 respectively engage the jack contacts lil5869 and the jack ring contact ii is automatically opened.

The tip spring 6? and sleeve 59' of jack 13 are connected through an I-l-pad 12 to a pair of transmission wires L2 and LI respectively, and the ring spring 63 is connected to the central point 13 of the pad. The jack contact H (usu' ally called the ring normal) is connected to one side of a line relay H, which isconnected on its other side to a positive battery terminal-l5. Consequently, a standby positive-potential is nor mally applied to lines LE-LZ at the transmitter through the relay id. However, the circuit of this relay is not closed at this time because it is open at the patronsmachine, 'as will appear later. It should be understood that a transmission pair LIL2 and a line relay it are associated with each one of the patrons line jacks IS. The line Ll-L2 operated on a simplex basis to carry not only the facsimile signals but also the battery control circuits. 7

In the normal or idle condition of the transmitter-that is, with theplug disconnected and no 'drumgin the machinethe battery power keeps two relays energized, namely, a double-coil relay l5 and a slow-release relay Tl. The normal energizing circuit of relay 16 goes from the plus battery conductor 18, wire 19, through the left coil 16a of the relay, and by wire Sll to ground through the closed contact 3! of a relay 82, which is not energized. The circuit of the right-hand coil 16b of relay 76 remains open until the relay Ill is energized. The circuit of relay 7? goes from battery lead 18, wire 33 and through the relay coil to ground. A shorting wire 84 connects wire 83 with the switch fill. When there is no drum in .themachine, the switch 4'! is open and the relay Ti is not shorted out by wire 84. It will thus be seen that nor mally the front contact 85 of relay it is closed and its back contact 86 is open, whereas the energized relay 1'! normally holds all three of its back contacts 81-88-89 open.

A cold-cathode gaseous tube fill has its plate anode 9| connected to one side of a relay 9?, the other side of which goes to contact 8'5 of relay 7. The starting anode 93 of tube 99 is connected to a wire 94, which is connected at one end to the armature contact of relay 92,.and

the other end of wire 94 goes to ground through a condenser-resistor network 99. It is thus clear that the circuit ofrelay QZgoes through the cold-cathode tube 99, so that this relay is energized only when the tube fires upon the application of sufiicient positive voltage to the starting anode 93. The conditions under which the firing of tube 99 occurs will be set forth in due course.

As previously mentioned, each transmitter has its own call button It for calling a patrons attention to his machine when a message is to be transmitted to him. This call button, as shown in Fig. 2, has five contacts numbered 91 to IcI. The contacts 98 and NI are movable Spring arms normally biased against their associated contacts 91 and I00, respectively. Contact 91 is connected by a wire I92 to a make contact I93 of a slow-release relay I94. The spring contact 98 is connected to conductor 66, which is one of the output leads of the regulator-inverter RV and goes to the sleeve 59 of plug 26. The normally open contact 99 connects by wire I95 to one side of the relay I94, the other side of which goes to the back contact I99 of relay 92. Contact I96 of the call button connects through wire I91 to contact I98 of relay 92, and the spring contact I9I is connected to wire 65 which connects one side of relay I9 to the ring 63 of plug 25.

When the operator at the central ofilce has a message to transmit to a certain patron, she wraps the sheet around the drum and then performs three manual operations in this order: first, she mounts the loaded drum in the machine; second, inserts the plug 26 into the patrons line jack I3; third, presses the transmitter call button I9. Now let us see what each of these manual operations does in the transmitter circuits of Figs. 2 and 3, without considering at this time their effect on the patrons transceiver.

The mounting of drum 29 in the machine closes switch 41 and short-circuits the normally energized relay I1 which releases all its contacts, whereby relay 52 is operated to turn the power on and conditions the machine for operation by energizing the drum motor 36, the chopper motor 37, and the exciter lamp 9| through transformer I09.

The insertion of plug 29 into jack I3 connects the output leads 64 and 68 of the regulatorinverter RV to the transmission wires L2 and LI, respectively, through the tip 97' and sleeve es of the plug. However, at this time the output loads 64 and 66 are short circuited by wires H9 and II2 through the closed switch 45 (Fig. 3) which remains closed until the scanning carriage has moved down a certain distance from start position.

Having inserted the plug, the operator presses the call button l6 for a second or two, then releases it. While the button is held down, the closed contacts 98 and '99 connect one side of relay I94 to line LI through wire I95, conductor 66 and through the plug and jack sleeves lit-$9. The other side of relay 'IIlllr goes through back contact I96 of relay 92 (not energized), wire H9, and through closed contacts IIE-il5 of relay II6 (not energized) to a source of negative battery I I1. This battery circuit goes through relay 19 and through I-I-pad 72 over lines Ll-L2 and is grounded at the patrons machine (as will be explained later), so that relay I9 1 is energized and closes its front contact I93 while the call button I6 is held down. It may be mentioned here that this negative potential put on lines LIL2 operates a buzzer at the patrons machine.

When the call button. Isis released, the negative potential applied to simplex lines LI--L2 through relay I94 is interrupted at the open contact 99, but relay I94, being slow to release, holds its contact I93 closed for a brief interval after release of the call button. Therefore, the closing of contacts 91-99 of the released button connects the lines LI-L2 to the positive battery lead I8 through the following connections: wire IIB, closed contact I93 of relay I94, wire I02, contacts Ell-98, conductor 66, the plug and jack sleeves 69-69 and the H-pad I2. This positive voltage (usually 129 volts) is maintained for a fraction of a second before the relay I94 releases.

The positive battery thus maintainedon transmission lines Iii-L2 is also impressed on the starting anode 93 of tube 95 through the resistors of pad 72 to the central point I3, through jack and plug rings 99'--53, wire 55, closed contacts Illll99 of the released call button, wire lei, closed contacts 198 and 95 of relay 92 (not yet energized) and through wire so to the resistor network 96 attached to anode 83. This positive potential causes the timer tube 99 to fire, so that plate current is drawn through the coil of relay 92 from battery lead 78 through closed Contact 8? of the deenergized relay ll. Relay is, therefore, energized and its opened back contact 88 breaks the connection between the lines Li-LS and the starting anode of tube 99.

With relay 92 energized, negative battery is again impressed on lines LIL2 from terminal II'I, closed contacts II 5Ill of relay I'IB (not energized), Wire H3, closed front contact II?! of relay 92, through coil of relay '39, wire 35 and through the plug and jack rings SW33 to line's LIL2. As before, this negative battery continues to sound the patrons buzzer until he responds by mounting a recording blank on his drum and closing the start switch of his ma chine. The energizing of relay 92 also closes the circuit of the associated red busy" lamp 58 to let the operator know that connection with the called machine has been made. When the relay I9 is energized, it closes its contact IIS to place a ground on relay 92 and cause it to operate for a purpose that will be explained in due course.

The reason for applying a positive potential on lines LIL2 after the first calling signal of negative potential has gone over is to test the system to determine if it is in condition to transmit from main office to patron. If, for instance, the patron has started his machine as a transmitter when the operator at the main ofiice releases the call button, the tube 9?] will not fire and the transmitter will not get through to the patron's machine. This fact would be indicated to the operator by the failure of the red busy lamp I8 to light, as will be fully explained later on. In that case, the operator would simply unplug the transmitter and plug in a recorder to receive the patrons message.

The circuit of patron/s machine We have learned What happens in the transmitter circuits at the main ofiice when the operator calls a patron to send a message to his machine. Let us see how the patrons machine responds to that call.

Referring to Figs. 4 and 5, the mechanism of the patrons transceiver is represented schematically by a scanning drum I28, an electric stylus I EI for transmitting and recording, a synchronous motor I22 for operating the drum, and another motor I23 for moving the stylus along the paper on the drum. A phasing commutator ii rotates with the drum and has an insulated segment l2 which a brush I26 engages briefly once for each turn of the drum. For the purposes of this description, it may be assumed that the construction of the patrons machine is like that set forth in the copending application of Ridings et al., Serial No. 33,354, filed June 16, 1948, to whichreference may be had for such structural details as are not necessary to show or describe in the present specification; I

The electric apparatus that goes with each machine includes (Fig. 4) a power supply unit PW, a; recording amplifier RP, a transmitting amplifier TP, and (Fig. 5) a set of control relays with circuits to be presently described. It may be assumed that the units PW, RP and TP are like those shown and explained in detail in the aforesaid application of Ridings et al. So it will sufiice here to present'those' electrical units in simplified form. Y

- The power unit PW is connected by a pair of conductors I21 and I28 to bu's bars A and B,

which represent a source of local power, such as the :usual 120 volts-60 cycle commercial supply. The conductors I21and I29 go to "the primary coil or" a transformer I29, which is connected to a suitable rectifier I36 for supplying direct current to the tubes of the amplifiers RP and TP. The voltage figures placed at the rectifier output terminals I3I and I32 are merely for descriptive purposes to indicate the voltages as used in a particular installation of our system. I The recording amplifier RPhas asignal input tube I35 and an output tube I36. The incoming signals are impressed on the grid I31 of tube I 35, and the amplified recording voltage goes into the circuit of plate I38 of tube I36; This will be presently explained in connection. with Fig. 5 and no further details of this amplifierneed be described for an understanding of oursystem.

For the same reason, we need only mention that the transmitting amplifierTP comprises a signal .input tube I39 and an output tube I46 which also functions as an oscillator'to provide carrier frequencyfor the, facsimilejsignals. The junction MI may be considered as the. input point of the facsimile. signals comingyfrom the-stylus I 2! when the machine operates as a transmitter. The .variable signalvoltage at point I lI goes through a bridge network I62 andis impressed at the proper level .on the grid I 43 of input tube I36. 1

As previously mentioned, the control circuits for each patrons machine are on asimplex basis over the transmission lines LI-+L2, which connect the machine with the main ofiice. Referring to Fig. 5, there is a line transformer Idtwhose coil I is permanently connected to the transmission pair LI- L2. The other coil I46 of transformer I is connected at one side by a conductor M1 to the rectifier terminal I32 of the power unit PW. The line transformer M l thus performs the double function of input and output transformer for the machine, depending upon whether the machine receives or transmits.

The center of coil I45 is connected by a wire to the center of two selenium or similar rectifiers I46 and I56, which are connected in series so that negative battery placed on the simplex circuit at the main office will cause current to fiow only through rectifier I46, While positive simplex potential will send current only through the other rectifier I59. The negative side cfrectifier I59 is connected to a line relay 'I5I and-the other side of this relay goes to a conductor I52, which is connected to the commuline relay I5I is energized,

k the patron places a tator brush I26 and also to a normally grounded relay contact I53. The positive terminal of rectifier I50 is connected through a resistor I53a. to a conductor I 531) which is grounded under certain conditions, as will be explained at the proper time. It will, therefore, be understood that relay I 5I is energized only when negative battery is applied to the simplex leads LI-LZ at the main oifice. This happens, as we saw in Fig. 2, when the operator inserts a transmitter plug 26 in the patrons line jack I3. Of course, the control circuits in the transmitter and the rectii'lers IS-I 59 can be so arranged that only positive battery will operate of battery polarity is within the invention. I g

The energizing of line relay front contact scope of our I5I closes its I55, which completes the circuit of a buzzer I55 through the following connections: From bus bar A over wire I55, relay contact I54, wire I51, through the buzzer coil, wire I58, closed contact I59 of a start switch I 69 (now in ofi" position), and through connection I 6| to bus bar B. Hearing the buzzer, sheet of recording paper on the drum I20 andmoves the switch I66 to on position, whereby the contacts I62 and I63 are closed and connect with bus bar B. The machine is now automatically set up as a recorder by cutting out the transmitting amplifier TPand placing the recording amplifier RP into service.

This automatic conditioning of the machine is accomplished through a pair of relays I64 and I 65, both ofwhich are connected at one side to a conductor I66 which terminates in the switch contact I63. The other side of relay I64 is connected by a wire I61 to a normally closed relay contact I68, wire I69, contact I10 of line relay I5! (whennot energized), wire H! to junction point I12, and by wire I56 to bus bar A. When the its contact I16 is opened and prevents relay I64 from operating upon the closing of switch I60. Because relay I64 is not operated, its contact I13 remains open and keeps the input conductor I14 of the transmitting amplifier .TP out of circuit. The other relay contact I13 is connected by a wire l1 i to the grid I31 of input tube I35 of the recording amplifier RP.

On the other hand, the closing of start switch I66 completes the circuit of relay I65 as follows: from bus bar A, conductor I56, wire I'II, closed contact I15 of the unenergized relay I34, wire I16, through the coil relay I65, wire I11, conductor I66 and through the closed switch contact I63 to bus bar B. The energized'relay I65 opens its back contact I18 and closes its front contact I19. The open contact I13 disconnects the wire I36 which goes to the transmitting amplifier TP, and the closed contact I19 completes the recording circuit from stylus I2I, through wires I6I and I82 to plate I38 of the output tube I36 in the recording amplifier RP.

Further, the closing of contact I33 of the en ergized relay I65 puts grounds on a conductor I85 which goes to the cathode I85 of input tube I35 in the recording amplifier. At the same time, the Opening of back contact I 86 ofrelay I65 removes ground from a conductor. I81 which goes to the cathode I68 of output tube I56 in the transmitting amplifier TP. Relay I65 looks through its closed front-contact H39 which connects with bus bar B through wires I96 and relay I5I. Such reversal I9! by way of a normally closed relay contact It is clear from what has been said that the mere closing of the start switch Ifiilin response tothe operation of, buzzer I55 from. the main office automatically places the patrons machine in condition to record. Theclosing of switch 559 cuts out the buzzer by opening the contact I59 and the closing of switch contact I33 completes the energizingcircuit of'transformer. I29 in the power unit PW. At the. same time, the synchronous motor I22 is started to operate the drum I29, but, the circuit of the stylus motor I23 is not closed untila heater relay I93 is operated. This. relay is connected by a wire Iflt to the cathode I95 of output tube ISt in the recording amplifier RP.

When the recorder tube I36 has heated sunlciently to draw current: across. the plate-cathode path, the relay, IE3. is energized and closes its front contact I,9I. The circuit: of stylus motor I23 is now closed from. bus barxA, wire I56, through closed contact I54: of energized relay I35 I, wire I51 to junction I3'I, wire .198, closed relay contact I96, through the windingsof motor I23, wire I99 and through the. closedswitch contact I53 to bus bar B. The relay; I93 willoperate in about twelve seconds after. the start switch we is closed. The purpose'of. this delay is to provide a shunt around the phasing commutator I2 -l by keeping the contact I53 grounded until the recording amplifier is' ready for use. In this way we prevent the starter transmission until the amplifier RP is in itsoperative condition.

The energizing of relay I93-opens its contact I53 and thereby removes the shunt from around the commutator I24 so that the negative simplex circuit through the relay I5I is opened briefly once for each revolution. However, a condenser 299 connected across the relay IEI- prevents its release during the short interruptions caused by the commutator I24. The effect of these circuit interruptions is to phase the transmitter drum at the main ofiice. To understand this, we have to go to Figs. 2 and 3.

It will be recalled (to review briefly the initial operations at the main office) that when the central operator pressed the call button I6 after plugging a transmitter into the patrons line jack l3, negative potential was placed on the simplex line LI--L2 from the battery source II'I through relay I94. At the patrons machine, this negative potential operated the line relayv I51. going to ground through the closed contact I53 of relay I93 (then unenergized) When the central operator released the call button, the negative potential on line LI-L2 wasmomentarily changed to positive and the relay 92. was ener gized from the positive battery lead I8 through the tube 99 at the momentit fired. The closing of relay contact IIB again caused negative battery to be impressed on line LI-L2, this time through relay I8, which was thereby energized. The patrons buzzer continued to sound until he closed his start switch.

Now, when the relay I93 at the patrons machine is energized and causes the commutator I24 to open the negative simplex circuit periodically on line LIL2, the relay I0 at the main ofiice (Fig. 3) starts to pulse in synchronism with the patrons drum I20. At each release, the relay I0 opens its contact I I9 and removes ground from relay 82, but this. relay is slow to release and therefore remains energized during the momentary interruptions of the circuit of relay I8. Sparking at the relay contact I I9 is prevented by accuses grounding the pulsating tongue H9 through a condenser 200'.

The energized relay 82 opens its back contact 8| and breaks the circuit of the left coil 'IEcof relay 16'. This relay does not release, however, because the circuit of its other coil II-ibis now completed through its own contact 85 and the closed contact 9 of the pulsing relay I0 during the energized periods of the latter. At the next break ofthe simplex circuit by the patrons commutator I24, the relay I9 momentarilyreleases and opens its contact I.I 9, thereby causing the relay I6 .to release. The closed contact 86 of relay 16' closes the circuit of phase magnet 35 from the, positive battery lead I8, wire. 201, through the magnet winding, wire 292, relay contact 8G and through the closed contact, 233 of the unenergized relay H6 to ground.

Let us remember that when the operator inserted the message holding drum 43 into the machine, the power relay 52: was: operated and energized the drum motor 35, the chopper motor 3? and the exciter lamp "3i. At the, same time the magnet 38 was released to allow the half-nut 33 to connectwith the feed screw 35-. However, the drum 43 was still held stationary by the locked clutch 49'. Now, when the phase magnet 39 is energized, it releases the clutch 48 and causes the drum 43 to rotate in phase with the patrons drum I20. With the scanning carriage SK starting to move down, the scanning of the message on the transmitter now begins. The facsimile signals transmitted over the line LI- L2 are recorded on the patrons machine by the stylus I2I in a manner well understood by electrical engineers- The .scanningprocess continues untilthe entire message on drum 43 has been scanned, whereupon either'the switch 44 or the contactor 34' will be closed, as previously explained. In either case the relay H6 will be energized from the battery lead 'I8, wire 204, closed contact 88 of deenergized' relay. 11, through the winding of relay I I6, wire ZMand through the closed switch 45 (or'contactor 44 to ground. The relay H6 locks through its ownjclose'd contact 205 to ground. One result "of relay I-IB being energized is to break the circuit of clutch magnet 39 at the opened contact 203, thus stopping the rotation of drum 29.

The tongue H4 of energized relay H6 breaks with contact H5 and closescontact 206, whereby the simplex line LI"--L2 isv switched from negative. to positive battery through the following circuit: from positive lead 18, wire 207, closed contact 208 of energized relay 82, through closed contacts 206 and H4. of energized relay H6, wire I I3, through closed contact. I I8 of energized relay 92, through relay I0, wire-.65, through the ring contacts 6868' of theplug and jack connection to center tap I3 of the H-pad'I2, and from there dividing equally over the wires LII-L2.

The positive potential thus impressed on the transmission lines at the main office releases the line relay IEI at the patrons machine, whereby a relay 299 is energized through the following circuit: from bus bar B, through contact I62 of the closed start switch I60, wire 2I0, through the coil of relay 209, wire 2'I I, closed contact 2I2 of energized relay I65, wire- 2I3, through closed contact 2M of the released relay I5I, wire 2I5, closed contact I75 of the unenergized relay I64, wire III to point I12, and by wire I56 to bus bar A. The energized relay 209 looks through its contact 2H; and through a normally closed switch 2H, which we call the acknowledge button. It should be noted here that when the relay 209 is operated its closed contact 2I8 maintains a ground on the positive simplex conductor I531: through the resistor [53s.

The closed contacts 2H3 and N9 of energized relay 299 operate the buzzer I55 through a circuit from bus barA wire I58 to point 220, closed contact 2I9, wire I51, through the buzzer winding to wire I58, through closed contact 2I9', and by wire I9I to bus bar B. At the same time, a lamp 22I lights through a circuit from bus bar A, wire I56 to point I12, wire I'H, closed contact I75 of unenergized relay I64, wire 2| 5, closed contact 2I i of the deenergized relay I5I, wire 2I3, closed contact 2i 2 of energized relay I65, wire 2! l to point 222, wire 223, through lamp HI and by way of closed switchZIl and wire IBI to bus bar B. While the lamp 22I is not really necessary, it combines with the buzzer to produce a visualaural signal to impress the attendant of the patrons machine with the fact that the message has been completed at the main oflice and that the machine should now be turned off.

It should be mentioned that the switch E86 is automatically shifted to ofi position by the slidable stylus carriage at the end of its path of travel. This operation is fully explained in the pending application of Ridings et al., Ser. No. 33,345, previously referred to. If the scanning of a short message is finished before the stylus carriage can complete its forward movement, the patron opens the switch I60 by hand. In either case, the operation of switch I 6!) to off position shuts off the power supply from everything except the relay 299, which remains energized to keep the buzzer I55 and lamp 22I going. The

attendant now removes the recorded message from the drum andoperates the acknowledge button 2!? to open position. This breaks the circuit of relay 239 to stop the buzzer and put out the light. The release of relay 209 opens the contact 2I8 to remove ground from the positive simplex lead I53?) and that operation has the following efiect on the transmitter at the main office.

As previously explained, when the end-of-message switch it (or 44) was operated at the transmitter, positive battery was sent through relay 70 over the simplex leads to the rectifier stack I ie-I58 in the patrons machine, whereby the line relay IEI was released and the relay 269 was energized. That placed a ground at relay con tact 218 on the positive terminal of rectifier I56, thus completing the circuit of the transmitter relay ll]. Therefore, the removal of ground from the positive conductor I53a by the deenergizing of the patrons acknowledge relay 2% automatically releases the relay H1 at the main office.

The release of relay i0 breaks the circuit of coil 16b of relay 1B and releases the relay 82, so that ground is placed on coil a and relay 76 is restored to its normal energized condition. With relay 82 released and relay H6 still energized, the red busy lamp i3 goes out and the patrons white acknowledge lamp I! goes on through a circuit including the closed back contact 22 2 of relay 82 and the closed front contact 225 of energized relay H6. The lighted lamp I! tells the central operator that the patron has removed the blank and operated the acknowledge button 2. The operator will now pull out the plug 25 and remove the drum from the machine. The removal of drum 29 opens the shorting switch 41 and again energizes the relay Tl, which opens all its contacts, thereby releasing the relay H6 '14 and extinguishing the lamp I7. The energizing of relay. "5'! breaks the circuit of the power relay 52 at the opened contact 89, whereby th motors 35 andtl are stopped and the magnet 38 is energized to remove the half-nut 33 from the feed screw As a result, the scanning carriage SK returns to start position and the transmitter is again in condition for the next operation.

As mentioned in an earlier part of this description, if a patron should happen to start his machine as a transmitter at the same time that the operator at the main ciiice is pressing the patrons call buttonIS to send him a message (or just before that button is pressed), in that event the red busy lamp I8 on the concentrator panel will not go on and the operator is thereby informed that the two machines have not made connection. This condition is due to the fact that the tube at in the main ofiice transmitter (Fig. 3) has not fired and accordingly the relay 92 has not operated. To understand this let us recall that when thecentral operator releases the call button i6, a positive potential is impressed on the starting anode 93 of tube 95 through a circuit previously traced. This positive potential causes the tube to'firc and energize the relay 92, which lights the redlamp it to inform the operator that the connection has gone through to the patrons machine.

Now suppose the attendant of the patrons machine, intending to send a message to the main ofiice, hasclose'd the start switch 69 before the central operator presses the call button. The patrons relay- I5I (Fig. 5) being unenergized under those conditions, the closing of switch 58% energizes the patrons relay its which sets the machine up as a transmitter. The relay I54 is energized from bus bar B through closed switch contact I63, wire I 66, through the winding of relay I5 3, wire I51, through closed contact I68 of relay I 93 (not energized), wire E69, through closed contact we of line relay, i5! (not energized) and by wire 156 to bus bar A.

The energized relay I64 closes its front con tact 225 which establishes a ground for the positive potential on the simplex leads LI-L2 through the following connections: from the positive terminal'of rectifier IMF, through resistor I 53a, wire 227, closed contact 226, wire H52 and through the closed relay contact I53 to ground.

This ground on the positive simplex leads prevents the positive voltage from building up high enough on the start anode 93 to fire the tube 98 at the main-onice, so that a connection will not be-made between the patrons machine and the main oiidce transmitter. This explains why the application of positive potential to the simplex 'line. after the first calling signal of negative pctential has gone over is an automatic test to see if the line'is clear for facsimile transmission to the patrons machine.

There is yet another detail that requires explanation in the transmission operation from main office to patron according to the system as disclosed in Figs. 3 and 5. We have assumed that the transceiver scanning mechanism represented schematically in Fig. 5 by the parts I20 to I23 is like that shown in the copending application of Ridings et al., Ser. No. 33,345, filed June 16, 1948. In that case the stylus is so mounted that normally it is held in raised position and is automatically lowered into scanning position at the proper moment. In Fig. 5, the normal raised position of stylus i2! is indicated at I2 I I It takes a certain interval of time (which may vary slightly in different machines) for the stylus to move down from raised t scanning position. This movement of the stylus starts at the moment when the stylus motor I23 is energized and that moment occurs, as we have seen, when the transmitter at the main office starts scanning. It is the function of the normally closed switch 45 (Fig. 3) to short-circuit the signal output leads and 66 until the scanning carriage SK has moved down a certain distance (according to the length of cam 48), and during this interval the stylus I2I in the patrons machine swings down into contact with the recording blank on the drum I20. Therefore, no signals can go over the line until the stylus I2I is in position to record. or course, with other designs of transmitters, the shorting switch 45 may not be necessary.

Transmission from patrons machine. to main ofiice We now come to the other operation of, our system, namely, sending a message from the patrons machine to a recorder at the main oflice. From the patrons standpoint, this operation is very simple. He places the prepared copy around the drum and moves the start switch I6Bto on position. That is all he has to do, for the machine now sets itself up automatically as a transmitter.

The closed contact I63 of switch I60 connects the power to the machine, energizing the drum motor I22 and the power supply unit PW through circuits previously traced. This time the relay IE4 is energized to cut out the recording amplifier RP by opening its contact I13 which is connected to the grid I2'I of tube I35, but the output tube I36 of this amplifier is energized from the power unit PW for the control of relay I93. The circuit of relay I64 goes from bus bar B through switch contact I63, wire I66, through the relay winding, wire I61, contact I68 of relay I93 (not energized), wire I69, through closed contact III] of relay I5I (not energized) and by wire i56 to bus bar A. Relay I64 looks through its contact 228 independently of relay I93.

The closing of contact I13 of the energized relay I34 connects the coil I43 of line transformer I44 to the transmitting amplifier TP, and the closed contact 226 of this relay places a ground through wire 221 on the positive side of the simplex circuit LIL2. This is important to rememher. It should also be noted that the recording relay I65 is not energized, whereby the cathode lead I84 remains open and the recording amplifier RF is kept out of service. The stylus I2I is now connected to the bridge circuit I42 of amplifier TP by way of wire I8I, closed contact I18 of relay I65 and wire I89. However, at this moment the stylus I2I is still in its normal raised position I2 I because the stylus motor I23 is not yet operating.

So far, then, the drum I520 is rotating atsynchronous speed, the transmitting amplified TP is in operative condition, but the scanning of the message has not'yet begun. We now go to the main ofiice and see what happened when the patron closedhis start switch.

Referring t v Fig. '7, the rectangle 239- may be assumed to represent a facsimile recorder of the continuouspaper feed type like that disclosed in the pending. application of I-Iallden and Zabriskie, Serial No. 83,333,.filed- March 25, 1949. For the purposes of this description, we have shown in symbolic form only such parts as are needed to explain the operation of our system. There is a flat stationary laten- 23I over which the recording paper 232 is continuously moved from a supply roll 2.33 by a feed roller 2'34 operated by a motor 235. A stylus 236 mountedon a belt 231 is driven rapidly in a straightline across the slowly moving paper by a motor 238. The connection between the stylus belt 237 and motor 238 are such that the belt is not operated until a. stop disk 239 is released by a magnetZtll when the latter is energized and moves its armature 24I away from the disk. For the present that is all we have to know about the recorder 230 at the main ofiice.

In Fig. 6, the line connections that go to the patrons jack I3 are the same as those in Fig. 2, previously described, so the same reference numerals are used for the corresponding parts in the two drawings. As already explained, normally there is a positive standby potential on the simplex line LIL2 from battery I5 through relay I4 and the ring 63' of jack I3, but this circuit is normally open at the patrons machine. Now when the patron closes his switch I69 to send a message, the closed contact 226 of energized relay I64 (Fig. 5) puts a ground on the positive simplex line LIL2 through the center tap wire I48, rectifier I59, wire I52 and grounded contact I53, whereby the circuit of relay I4 at the main oifice is closed. The energized relay I4 closes its contacts 242 and 243 with the following result.

Referring to Fig. 6, the closing of contact 242 lights the lamp I4 that appears directly over the patrons jack I3 on the concentrator panel (see Fig. 1.). The closed contact 243 energizes a large signal light 244 which is common to all the patrons machines and is preferably placed in a conspicuous position on the concentrator panel I2 (Fig. 1). If the operator happens to be away from the panel when a patron sends in a call, the light 244 will attract her attention. We may also add a buzzer 245 which sounds when the lamp 244 goes on. For this purpose, we provide a relay 246 which operates when the energized line relay I4 closes its contact 243. The closed contact 241- of energized relay 246 completes the circuit of buzzer 245. if the hand switch 248 has been closed. By opening this switch the buzzer is cut out of, use.

The main oflice operator, seeing the light I4 over the patrons jack I3, plugs in a recorder and presses the start button I9 associated with that particular machine. When the plug 21 is inserted in the jack, the standby positive potential over the line through relay I4 is disconnected at the opened ring contact 68 of the jack, and the relay I4 is deenergized so that the lamp I4 goes out. The operation of start button I9 energizes a relay 259 (Fig. 7) from positive battery source 25I through normally closed switch contacts 252-253, wire 254, through the winding of relay 2.59, start button I9, wire 255, to ring contact 255 of the inserted plug 21, and by way of the ring normal 68. of jack I3 and H-pad 12. over the simplex line LIL2 to the patrons machine. Here (Fig. 5) the positive simplex goes over line I48 through the rectifier I59, resistor I53a, wire 221, and by way of the closed relay contacts 226 and I53 to ground.

At this time the patrons relay I93 (Fig. 5) is not yet energized because its circuit goes through the tube I36 which takes about ten to twelve seconds to heat, as previously mentioned. When the relay I93 operates, the ground at its contact IE3 is lifted and now the circuit of relay 250 at the main ofiice recorder goes to ground by way of the patrons rotatin commutator I24. Therefore, at each revolution of the patrons drum The closed contacts 265 of relay 258- cause the power relay 266 to be energized'f-rom battery 259, wire 260, through the 'coil of relay.266, wire 261, and through contacts 265 to the grounded conductor 264. The closed contacts 2680f relay 258 short out the start button I9, so that, when the button is released, the positive simplex circuit through relay 250 remains closed.-

The energized power relay 266 closes its contacts 2'66 which light the red busy -1am'p'2I and connect the power mains A and B-to -a recording amplifier RM. Since this amplifier does not by itself constitute a partof our invention, it is suificient to show it merely in schematic form with a power input transformer 269 which is connected by leads 218 and 21I to the power source A B and supplies current to the tubes in the amplifier when the relay 266 is energized. The signal input leads 212-213 of the amplifier go through an adjustable T-p'ad 2-14 to the tip 215 and sleeve 216, respectively, of the inserted recorder plug 21. The amplified signal output of the amplifier goes through=1ines211 to the primary coil 218 of a transformer 219, whose other coil 280 is connected at one side by a wire 28I to the recording stylus 236. Theother side of coil 286 is grounded. The output leads 211' are normally short-circuited by wires. 21.1 which go tonormally closed relay contacts 282.

The closing of relay switch 266'ralso energizes the stylus motor 238 frombus bar B, Wire 282, through the motor windings, wire 283, and through switch;266' to bus bar A. I-Iowever, the stylus belt 231 is not. yet moving because the stop disk 239 is held locked by the armature 24I of the unenergized magnet 246. 1 z

When the energized relay 258 opens its back contact 284, it removes. one ground from the right-hand coil of a two-coil relay 285,,which is normally energized from battery 259, .through wire 286 and the closed contact 284 which goes to ground through the tongue 284' before the relay 258 is energized. The opening of relay contact 284 does not, howeveigrelease the relay 285 becauseat this time there is another ground on the right hand coil from wire 286, through the closed contact 281 ofa normally'energized relay-288, and by wire 263to the grounded conductor 264. Besides, the second or left-hand coil of relay 285 receives battery from source 259 through its own clo'sed contact 289, wire 296, closed contacts-29I-292 of energized relay 250 (not yet pulsin'ghthen to conductor 293, closed contacts 294' of relay 285, wire295,-'closed con-.- tacts 296 of a relay 291 (not-energized) and'by wire 298 to ground at 299. The relay 291 is of the slow release type and its function will presently appear.

We are to remember, then, that the normally energized relay 285 has remained energizedi so far; (that is, before the relay 250 starts pulsing from the patrons commutatorI24), even when 18 the contact 284 of the energized relay 258 is opened. The closing of contact 300 of relay 253 by the grounded tongue 284' places a shunt across the coil of relay 288, which is normally energized from battery source 30I and'through wire 263 to the grounded line 264. Being thus shorted out, the relay 288 is deenergized, but it is slow to release and after about one second it opens its contacts'281, thereby removing the second ground from the right-hand coil of relay 285 and thus causing that coil to become deenergized.

The relay 285 is now energized only by the left-hand coil and is thus in a condition to release as soon as the relay 259 starts .pulsing. That happens afterthe patrons relay'l93 (Fig. 5) has operated and removed the shunt from around the commutator I24. Therefore, when the next revolution of the commutator opens'the positive simplex circuit through relay 250 as previously described, this relay will momentarily release and open its contacts 29I-.-292. This breaks the circuit of the second or left-hand coil of relay 285, which thereuponreleases and through its opened contacts289 it breaks the circuit to contact 29I of relay 250. Consequently, the further pulsing of relay 256 will not affect the released relay 285.

The release of relay 285 causes several automatic operations to take place. The opened contacts 282 remove the short circuit 211 from the output leads 211 of .the recording amplifier, so that the received signals now can go through the transformer 219 to the recording stylus 236. The

closed relay contacts 382 complete the circuit of,

the paper feed motor 235 from bus bar A, closed relay switch 266', wire 283,. through rel'aycontacts 362, wire 364, and throughthe motor windings to bus bar B. The closed contacts 305 of released relay 285 complete the circuit of phase magnet 246 from battery 259 whereby the arma ture 24I releases the stop disk 239, and the stylus belt 231 is now driven by the motor 238, which was energized upon the closing of relay switch 266. The operation of armature 24I moves the adjacent switch arm 253 against a contact 306 which is connected to a source of negative potential 301. The simplex circuit through relay 258 is now changed from positive to negative. At the patrons machine (Fig. 5) this pulsating negative potential on the line operates the relay I5 I, which is prevented by the condenser 268'from releasing when the circuit is briefly interrupted by the commutator I24. The closing of relay contact I 54 completes the circuit through the stylus motor I23 from bus bar A, wire I56, closed contact I54 of energized relay I5I, wires I51 and I98, closed contact I96 of the energized relay I93 through the motor windings,wire I99, and through contact I63 of the closed start switch I60 to bus bar B. Thus, the scanning process is started at the patrons machine and continues until-the stylus has scanned the entire message, whereupon the switchIBIl is automatically moved back to ofi position. ,This automatic opening of switch I66 is fully described in the pending application of Ridings et al., Serial No. 33,345, previously mentioned.

During the scanning of the patrons message by stylus I2I, the facsimile signals produced by the contact of the stylus on the rotating message blank in a manner well known are impressed on the, grid I43 of the input tube I39 in the transmitting amplifier TP. This circuit goes from stylus I.2I through wire I8I, closed-contact I18 of relay I65 (not energized), wire I 80, and through the bridge network I42 to grid 143. The amplified signals are impressed on the transmission lines LI -L2 through the transformer I45. Let it be noted that during transmission of the patrons message the negative potential remains on the simplex line without interfering with the facsimile signals. 7

At the main ofiice (Fig. 6-) the received facsimile signals pass through the tip 2*:5 and sleeve 216 of plug 2'! over lines 212 and 213 into the recording amplifier RM. Theamplified signal output goesover the leads 211 through transformer 219 to the recording, stylus 235 (Fig. 7) whichrecords the message line by line on the slowly moving paper 232. This electric recording process on specially prepared paper is well understood and requires no, explanation here.

When the transmission on, the patrons ma chine ends. bythe opening of switch I53 (Fig.

the poweris disconnected sothat all relays are released andthe drum I23 stops. The release of relay Hid opens, the contact 226 and thereby disconnects the positive simplex lead 227. The stopped: commutator I24 ceases to interrupt the simplex circuit and causes the relay 250 at the main office (Fig. 7) to remain energized without pulsing. Under these conditions the contact 338 of'relay253 remains open and this contact is connected by'wire 295, closed contact 296 of relay 231 (not energized) and wire 238 to the control grid 399 off a. vacuum. tube are, which is shown as a pentode'. Theplate 3| l andscreen grid 312 of this tube are connected; to. theopposite sides of the slow-release relay 231. The circuit of control grid" 3139 contains a condenser 313 and a resistor 3l"4',.which go to. ground at 299. of the tube 315' is heated by a transformer 315 connectedto the bus bars A-B.

The left side of relay 29? and screen grid 3!2 are connected by a wire 3:19 to a source of. positive potential 323 through a normally closed switch 32l, but the relay: circuit is not closed until the tubelllfl draws current. This tube can not fire as long asthe control grid 35%] is connectedtonegative potential from a battery terminal 322. This negative potentialis impressed on grid 339' through either one. of two paths from the negative lead: 293 to wire 295. One path goes through the closed contact 308 of relay 250' when the latter is not. energized and the other path goesthrough the closed contact 294 ofirelay 285 when, the'same is energized, asit normally is. Both of those-negative potential paths'go through theclosedcontact 2950f relay 291 when the same is-not energized:

Since the two-coil relay 285' became deenergizedjustbefore the patrons machine started. to transmit, the only path for the negative potential to reach the-grid 3030f tube 3 l 0 goes through the contact 308 of relay'250 which pulses continuously during transmission; However, the opening of contact 333 during the energized periods of the pulsing relay 250 is too brief to causeremoval of the negative potential from the'grid 359- because the condenser 313, which is charged during the release of relay a,- keeps negative potential on the grid whenever the pulsing: relay opens its contact. 308.v Therefore, the tube 319 is kept fromfiring during the transmission period and thus the relay 291 remains unenerg-ized.

However, when the relay 250 steps pulsingand stays energized at the close of transmission from the patrons machine, the contact 338 remains open long enough; (less than two seconds is sum- The filament 20 cient in our present installation) to remove the negative potential from grid 3B3. Instantly the tube 3l0 fires and relay 291 is energized, thereby opening its back contact 296 and closing its front contacts 311 and 3l8, both of which when closed are connected to the grounded conductor 264-.

The operation of the end-of-message relay 291 at the main ofiice recorder has the following results. The closing of contact 3|"! places a ground on the right-hand coil of relay 285, which is now energized from battery lead 259. The energized coil 285 opens its contacts 305 and breaks the circuit of phase magnet 249', which releases its armature 24l, thereby locking the disk 239 and connecting the switch member 253 to the positive bat tery terminal 25!. At the same time the opened relay contacts 302 stop the paper feed motor 235.

It will be recalled that when the relay I64 at the patrons machine (Fig. 5) was released at the end of the transmission, the positive simplex lead 227 was opened at relay contact 226, Consequently, when the deenergized phase magnet 240 at the main office (Fig. 7) released its armature 24l and reversed the simplex potential from negative to positive, the simplex current through relay 250 dropped to zero, so that this relay new releases. Its open contact 25'! releases the relay 258, which opens its contact 398 and thereby causes the relay 288 to resume its normal energized condition. The opened contact 265 of relay 258 breaks the circuit of power relay 263, causing the switch 236' to open. The red busy lamp 2! is now extinguished and the end-of-message lamp 29 .is lighted from the battery terminal 328 through a normally closed switch32l, wires 3I9 and 322, through the lamp to wire 323, closed contact 324 of the deenergized relay 25B, and through closed contact 3l8 of energized relay 29'! to the grounded connection 264;

When the end-of-message lamp 20 lights, it indicates to the operator that the patrons machine has shut down and that the plug 21 should now be pulled out; In the particular form of recorder shown diagrammatically in Fig. 7 there is a cam disk 325 which the operator turns by hand to feed out. the correct length of recorded paper from the platen 23!. This is done during one turn of the cam disk 325, as fully explained in the pending application of Hallden and Zabriskie, Serial No. 83,333, to which we have previously referred. For the present description we need only mention that when the operator has fed the recorded message out of the machine on a predetermined length of paper, the cam disk 325 opens the switch 32 I. This releases the end-of-message relay 291 and extinguishes the lamp 20. The recorder is now in standby condition for the next operation;

Broadly speaking, the tube 318 operates as a pulse detector at the main onice. end of our system to indicate whether a patrons connected machine is running. As long as the patrons drum is rotating, the commutator I24 keeps the relay 255 in the main oflice'recorder pulsing. And, as we have seen, the pulsing of relay 259 prevents the operation of tube 3H1, so that the relay 294 remains unenergized and the lamp 20 stays unlighted. Therefore, the unlighted lamp 2!! acts. as a signal to the operator that the patrons drum is running. Now, whenthe patrons drum stops rotating for any reason (as at. the: end of a message or due to a breakdown)", the relay 250 stops pulsing, the tube 3i Ii draws current and energizes the relay 291-,

which lights the lamp 2Il-as asignal' that the patrons machine has shut down. v

Synopsis of operation when main ofiice transmits to patron In view of the long description required to explain the operation of our system indetail, we shall summarize the essential events that take place in order to afiord a quick review of our invention. a v

First, the transmission ofa message from the main office to a patron (Figs. 2-3 and Figs. 4-5). The message is placedon the -drum 29 which is then inserted into the transmitter. Thisautomatically closes the switch 41 and shorts out the relay l1 (normally energized), thereby causing the power relay 52 to operate.- Power from the bus bars A--B is now connected to the regulator-inverter RV, the energized halfnut magnet 38 is released, and the drum motor36, the chopper motor 37, and theexciter lamp 3I are all energized. The drum 29 is not yet rotating because the disk 40 is still locked. V

The operator now plugs the transmitter into the patrons jack and presses the call button I6 associated with the connected transmitter. This places negative calling battery on"lirles LI-L2 while the button is briefly held down; When the button is released, the negative potential on the line is momentarily changed to a positive testing potential'which operates the relay 92 through tube '90 and lights the red busy lamp I8 after connection" with the patrons machine has been established. The energized relay 92 changes the positive potential back to negative on the simplex line, and this negative potential goes through relay I which is thereby energized.

At the patrons machine this negative potential operates a relay II and sounds the buzzer I55. The patron places a sheet of recording paper on his drum and closes the start switch I60. This connects power to the machine and automatically sets it up as a recorder by energizing the relay I65 and the recording amplifier RP. The drum motor I22 is started, but the stylus I2I is held inoperative for several seconds until the heater relay I93 is energized. The stylus motor I23 is now started and the commutator I24 causes the negative simplex circuit on the line to be opened briefly for each revolution of the drum shaft. The patrons machine is now ready to receive. a

1 At the main oflice transmitter, the interrupted simplex causes relay to pulse and the next break in this circuit will release the energized phasing relay I6. As a result, the phase magnet 39 is energized to release the disk 40, whereby the transmitting drum 29 rotates in phase with the patrons drum I20 which records the received message.

After the entire message has been scanned at the main oiiice, relay H6 is energized by the automatic closing of switch 44 and positive bat- .tery is now applied through relay I0 to the simplex line. The operation of relay IIG opens the circuit of phase magnet 39, whereby the disk 40 is again locked to stop rotation of the transmitter drum 29.

At the patrons machine, the positive potential onthe simplex line releases the relay I5I, causing relay 209 to operate. This sounds the buzzer I55. and lights the lamp 22I to let the patron know that the message has been completed at the main oliice. The patron will now open the :start switch I60, remove the recorded message,

and press the button 2I7 to acknowledge receipt of the. message. The operationofbutton 2I1 deenergizes the relay 209, which thereby removes ground from the positive simplex lead that goes through the rectifier I50. The machine is now entirely shut down and ready for the next operation, either for receiving or transmitting. I

At the main office, the removal of ground from the positive simplex lead by the operation of the patrons acknowledge button 2 I1 causes the relay 10 to release with the result that relay I6 is again energized and relay 82 is released. .This extinguishes the red busy lamp I8 and lights the white lamp I! to advise the operator that the patron has removed the recorded message and operated the acknowledge button. The operator now pulls out th plug and removes the drum 29 from the transmitter. Removal of the drum opens the switch 4'! and again energizes the relay 11, which releasesthe end-of-message relay IIS and puts out the lamp II. At the same time the power relay 52 is released and stops the motors 3B and 37, while the half-nut magnet 38 is energized to release the scanning carriagefor return to start position.

Should the patron, after receiving the signals I55 and 22I, fail to operate the acknowledge button 2|! within a reasonable time, the supervisor at the main ofiice can release the patrons relay 209 and turn ofi the signals by pressing the call button I6. This applies negative battery to the line, as previously explained, and energizes the patrons relay I5I, which breaks the circuit of relay 209 and completely shuts down the patrons machine.

Synopsis of operation when patron transmits to main ofiice After mountin the message on his drum-the patron closes the start switch I50. This connects power to the transmitting amplifier TP. The drum motor I22 starts rotating and the relay IE4 is energized. This automatically sets the machine up as a transmitter by connecting the stylus I2I to the input of the amplifier TP and connectmg the amplifier output to the line transformer I44. The stylus I2I remains'in normal raised position I2I because the stylusmoto-r I23 has not yet been energized. The, operation of relay I 64 places a continuous ground on the positive simplex conductor 22! through relay contact. I53.

At the main office (Figs. 6-7), the ground thus placed on the positiv simplex lead completes the circuit from positive battery 15 through the line relay M, which lights the lamp I4 over the jack of the calling patron. Seeing this light, the operator plugs in a recorder I button I9, whereby the relay 74 is released to extinguish the lamp and the relay 250 is energized from positive battery which goes over the lines LI-L2. The energized relay 250 causes relay 258 to be energized and this operates the relay 266 which connects the power to recording amplifier RM and starts the stylus motor 238. However, th stylus belt 231 is not yet running.

At the patrons machine, the heater relay I93 is operated after several seconds and connects ground to the positiv simplex circuit through the rotating commutator I24, whereby the simplex circuit is momentarily opened at each revoluand presses the start response to the opening of the simplex circuit of direct current potential.

relay 258 releases during the first break in the simplex circuit, thenorrnally energized relay. 285 releases to operate the paper fee-d motor 235 and the phase magnet 2%. The energized phase magnet releases the stylus belt 23'! for operation by motor 238 and at the sam time reverses the simplex potential from positive to negative. This negative potential remains on the line during the transmission cycle.

At the patrons machine, the negative simplex potential operates the line relay $55, which completes the circuit through the stylus motor I23, whereby the stylus I22 is moved into scanning contact with the message on the drum. The scanning process now begins at the patrons ma.- chine and the transmitted signals are recorded atthe main office. When the entire message has been scanned, the patrons switch I68 is auto-- matically moved to ofi position, whereby all power is disconnected and the machine is shut down, except that the line relay l5! remains energized by the negative potential on the line.

At the main office, when the patrons commutator ceases to interrupt'the simplex circuit, the relay 250 remains continuously energized and causes the operation of relay 291. This de-ener- .gizes the phase magnet 24s and changes the simplex potential from negative to positive, thereby releasing the patrons relay l5! and the relay 255 at the main ofifice. The release of relay 250 deenergizes the relay 258, which in turn causes the operation of relay 25'! and the release of power relay 2%. The red busy lamp I9 is new extinguished and the end-oi-nessage lamp 213 goes on. The operator now unplugs the recorder and pulls out the correct length of paper from the machine, thereby opening the switch 32L This releases the relay 2&7 and puts out the lamp 2a.

In this description of our invention we have referred to certain constructions of transmitter, recorder and transceiver as disclosed in th copending applications herein identified. However, it is to be understood that our two-way facsimile system is not limited to any particular construction of machine either at the main ofiice or in the patrons offices. It is only necessary that the machines used are capable ofoperating with the novel circuit controls embodied in our invention as described in the appended claims.

It goes without saying that the drawings represent only one iorm of our invention, which is capable of various changes and modifications within the scope of our claims. For brevity and cle arness in the claims we have used the terms positive battery? and negative battery in the broad meaning of battery of one polarity and battery or" the opposite polarity. As previously stated, where we now use negative battery we can use positive, and vice versa, so that these polarity terms are to be regarded as interchangeable both in the description and the claims. Obviously, by the term battery we include any suitable source Also, when we speak of a call button or start button in the claims, we mean any practical form of hand switch for the operator at the main office, thereby avoiding confusion inthe claims between the patrons start switch and the switches at the main oilice.

The specific circuits and apparatus that we have shown and described representa practical embodiment of our system asactually built and operated. This does not mean, however, that our invention is restricted to the details set forth, for the scope or" our invention as defined in the claims herein comprehends various changes and 24 modifications that may be resorted to by those skilled in the art. T f 1 We claim as our invention:

1. A two-way facsimile telegraphsystem comprising a transmitter'and a recorder at a central telegraph office, a distant transceiver constructed to transmit and to record messages, a pai-rof lines connecting said transceiver to switch terminals at the central office, means for connecting said transmitter to said switch terminals and other means for connecting said recorder to said terminals, relay controlled-circuits responsive to the connecting of said recorder to said switch terminals 'for automatically placing the recorder in communication with said-transceiver to record the facsimile signals transmitted by the trans" ceiver, and relay controlled circuits responsive to the connecting of said transmitter with said switch terminals for automatically placing the transceiver in condition to record the facsimile signals transmitted by the connected transmitter.

2. A two-way facsimile telegraph system comprising a transmitter'and a recorder at a central telegraph office, each of said machines having a connecting plug and a start button ,'a patrons transceiver constructed to transmit and to record messages, a start switch for said transceiver, a communication line for connecting said transceiver with a jack at the central oflice, means whereby the insertion of the transmitter plug into said jack and the closing of the transmitter but- 0011 when the transceiver switch is oil automatically conditions the system to transmit a message from the central transmitter to the patrons machine upon the closing of the transceiver switch, and means whereby the insertion of recorder plu into said jack and the closing of the recorder button after the closing of the transceiver switch automatically conditions the system to transmit a message from the patron's machine to the central recorder.

3. In a two-way facsimile telegraph system between a central telegraph ofiice and a distant tramceiver constructed to transmit as well as receive messages, a transmitter and a recorder at the central office, a communication line connecting the transceiver with a jack at central ofiice, said transmitter and recorder having each a plu for insertion in said jack, a start switch for said transceiver, means atcentr-al for placing battery on the line, a relay in said transceiver connected to be energized by the line battery when either plug is inserted in the jack, circuit connections whereby the transceiver sets itself up as a recorder when said relay is energized by insertion of the transmitter plug before said switch is closed, and other circuit connections which cause the transceiver to set itself up as a transmitterupon the closing of said switch provided said relay is then in unenergized condition.

4. A facsimile telegraph system comprising a patrons transmitter and a recorder located at a main telegraph ofiice, a communication line between said transmitter and a jack at the main ofi'ice, a start switch for said transmitter, a start button and a connecting plug for said recorder, means at the main ofiice for normally keeping positive battery on the line through said jack, a relay at the transmitter adapted to keep. said line battery normally open, means for energizing said relay whentthe transmitter switch is closed, said energized relay closing the circuit of said line battery, a call signal at the main office energized by said closed battery circuit, means whereby the insertion of the recorder plug in s'aid jack 25 and the operation of the recorder button automatically places the recorder in operative condition and puts negative battery on the line, and means at said transmitter for causing the negative battery to start scanning operation of the transmitter.

5. In a two-way facsimile telegraph system, a facsimile machine having control apparatus which includes a first relay normally energized to hold the machine inoperative, a second relay in said apparatus normally unenergized, a distant transceiver adapted to be operatively connected with said machine through a communication line, the scanning mechanism of said transceiver including a rotary drum, means for initially placing steady battery on the line through said second relay, control circuits at said transceiver for causing the second relay to pulse in synchronism with said drum, means for causing the pulsations of the second relay to effect the release of said first relay, and devices responsive to the release of said first relay for starting said machine in phase with the transceiver.

6. In a two-way facsimile telegraph system, a transceiver capable of transmitting and recording messages, the scanning mechanism of said transceiver including a rotary drum, a transmitting amplifier and a recording amplifier for said transceiver, means whereby only one amplifier at a time is operatively connected, a relay connected in a cathode circuit of one of said amplifiers whereby said relay is not energized until the connected amplifier is in operative condition, a facsimile machine located at a main telegraph ofiice and adapted to be operatively connected to said transceiver, control apparatus for said main ofiice machine including a relay, means responsive to the timed energizing of said transceiver relay for causing said main office relay to pulse.

synchronously with the speed of the transceiver drum, and means whereby the pulsations of said last mentioned relay phase the main oflice machine with said transceiver. I

'7. In a facsimile telegraph system, a main offic'e transmitter and a patrons recorder adapted to be operatively connected through a communication line, means at the transmitter for sending negative battery over the line before the transmittin-g operation starts, a call signal at the recorder operated by said negative battery, a start switch for said recorder, means for stopping said signal and turning the power on when said switch is closed, electric circuits operating in response to the closing of said switch for starting the scanning operation of said transmitter, means at the transmitter for automatically placing positive battery on the line at the close of the scanning operation, and means at the recorder for causing said positive battery to operate said signal as an indication that the facsimile transmission is complete.

8. In a facsimile telegraph system, a patrons facsimile machine for transmitting messages to a main telegraph ofice, a recorder at said office, switch means for connecting said recorder to the patrons transmitter over a pair of wires, means for automatically placing positive battery on said wires in response to the operation of said switch means, a relay in said recorder energized by the positive battery, means at the patrons machine for causing said relay to pulse at a predetermined rate in the positive battery circuit, apparatus in said recorder controlled by the energized periods of said pulsing relay to connect power to the recorder, other apparatus in said recorder controlled 26 r by the deenergized periods of said pulsing relay to phase the recorder and change the positive battery to negative battery on the line, and-mechanism at the patrons machine utilizing said negative battery to'start the transmission.

9. In a facsimile telegraph system, a transmitter having means for removably supporting a scanning drum, a movable scanning carriage operatively associated with said drum, a relay normally energized to keep the power off the machine,

means responsive to the presence of a drum in the transmitter for releasing said relay, a power circuit energized by the release of said relay, a normally energized magnet released by the deenergizing of said relay to condition the scanning carriage for operation, a normally deenergized magnet for holding said carriage against movement, a distant receiver having equipment for connecting it to said transmitter, a start switch at the receiver, recording apparatus in-the receiver energized by the closing of said switch, and apparatus at the transmitter controlled by the closing of said receiver switchfor energizing the second magnet. to

release said carriage for scanning.

10. In a facsimile telegraph system, a transmitterlat a-main telegraph office having-aplug to be inserted in a jack, a call button and a signal lamp associated with said transmitter, a circuit for energizing said lamp, a patrons transceiver normally in receiving condition, a start switch for said transceiver, a relay in said transceiver energized by the closing of said: switch to set up the transceiver as a transmitter, means whereby the energized condition of said relay when the call button at the main oflice is operated prevents the energizing of said signal circuit as an indication that the patrons machine'is in transmitting condition and incapable of receiving a message, and apparatus in said transmitter automatically operative when the transceiveris in receiving condition upon insertion of said plug and the operation of said call button to place the mainoflice transmitter in condition to transmit a message to the patrons machine, said apparatus including means to light said lamp as an indication that the two machines are operatively connected.

11. In a facsimile system, a transmitter provided with scanning mechanism which includes a rotary drum, a distant receiver adapted to be operatively connected with said transmitter through a communication line, said receiver having recording mechanism which includes a rotary drum, a start switch and a call signal for said receiver, means at the transmitter for placing battery on the line, a relay atthe transmitter energized by said battery, a relay at the receiver also energized by said battery to operate said call signal, means whereby the closing of said switch operates the receiver drum and causes said transmitter relay to pulse in synchronism with said drum, and apparatusat the transmitter responsive to said pulsing relay for starting the transmitter drum in phase with the receiver drum.

12. In a facsimile telegraph system, a. transmitter at a main telegraph. oflice for sending messages to a patrons transceiver over a pair of Wires, a call button at the transmitter, means for sending negative battery over the wires while the button is held down, circuit connections whereby positive battery is momentarily applied to the wire when the button is released, a normally open ground at the transceiver for holding said positive line battery inoperative if the transceiver is in condition to record, means at the transmitter for changing the momentary positive battery on the 

